[1][2][3] Montesinos' career was marked by his deep connections with the U.S. Central Intelligence Agency (CIA), through which he received substantial funding ostensibly for anti-terrorism efforts.

Investigations unveiled Montesinos' involvement in a wide range of illegal activities, including embezzlement, drug trafficking, and orchestrating extrajudicial killings.

Despite his imprisonment, Montesinos continued to influence Peruvian politics and sought to protect allies within the Fujimorist faction, including Keiko Fujimori.

[11][10] He would also serve as an aide for prime ministers Guillermo Arbulú Galliani and Jorge Fernández Maldonado Solari during the government of Francisco Morales Bermúdez.

[12] In 1974, political scientist Alfred Stepan of Yale University recommended to the Embassy of the United States, Lima that Montesinos be given the International Visitor's Leader Grant, describing him as the "most theoretically sophisticated of young military officers in national security doctrine" and that he had "considerable leadership potential".

[9][13] Montesinos expressed during the nomination process that he wanted to meet with officials of the Central Intelligence Agency (CIA) and the United States National Security Council of President Gerald Ford to discuss military and economic relations.

In 1977, Major José Fernández Salvatteci of the Army Intelligence Service (Spanish: Servicio de Inteligencia del Ejército (SIE)) charged Montesinos with the crimes of spying and treason, accusing him of delivering military documents to the embassy of the United States in Lima.

Locked in the Cold War with the Soviet Union and fearing its influence in the region, as well as that of the Communist government of Cuba, the US was seeking information about activities in Peru.

Between 1980 and 1983, Montesinos revealed sensitive information related to military wiretapping and assassinations to the newspaper Kausachum, run by Augusto Zimmerman, ex-spokesperson of deposed president Juan Velasco Alvarado.

[18][20] Fujimori's campaign exploited the popular distrust of the existing Peruvian political establishment and the uncertainty about the proposed neoliberal economic reforms of his opponent Vargas Llosa.

[22] Rospigliosi writes that head of the National Intelligence Service (SIN), General Edwin “Cucharita” Díaz, beside Montesinos also played a key role with making Fujimori abide by the military's demands.

[24][25] The United States reportedly maintained a relationship with Montesinos as a way to have direct influence in Peru; the SIN head would clear bureaucratic obstacles and would immediately implement the recommendations of the CIA.

[13] US Ambassador to Peru Dennis Jett told the Fujimori government that "any appearance of succumbing to French pressure would feed rumors of corruption in the Peruvian judicial system and thus scare off international investors", with Montesinos later telling a supreme court judge tasked with decision that if the decision was not in favor with Newmont, then the United States would not support Peru's territorial dispute with Ecuador from the Cenepa War.

On 16 March 1998, former Peruvian Army Intelligence Agent Luisa Zanatta accused Montesinos of ordering illegal wiretaps of leading politicians and journalists.

[13] Allegations circulated that Montesinos and General Nicolás Hermoza Ríos, the chairman of Peru's joint chiefs of staff, were taking protection money from drug traffickers.

[33] The scandal remains a mystery to this day because the drug's origin and destiny were never determined and the investigations were compromised by Fujimori's corrupt government and possibly Montesinos himself.

Recordings of radio communications presented during the trial showed that members of the army had let Chávez's organization operate freely in the Huallaga region in exchange for bribes.

[citation needed] After sentencing, while in prison, Chávez talked to the press and revealed that Montesinos said to him at one point that he "did some work" with Pablo Escobar, leader of the Medellín Cartel.

As proof, the government presented recordings during Chávez's trial of radio communications between his drug traffickers and members of the Armed Forces attesting to bribery of Montesinos.

[35] In addition, Chávez said that retired general Nicolás de Bari Hermoza, the former chief of the Armed Forces Joint Command, and Fujimori had both complete knowledge of the illicit acts of Montesinos.

[13] On 14 September 2000, Peruvian television broadcast a video of Montesinos bribing an opposition congressman, Alberto Kouri, to support Perú 2000, Fujimori's party.

On 29 January 2024, Montesinos pleaded guilty to charges of homicide, murder and forced disappearance in the 1992 killings of six farmers accused of being rebels in Pativilca, Lima Region,[40] and was sentenced to 19 years' imprisonment.

Prime Minister Carlos Ferrero and other prosecutors believed that the total amount embezzled by Montesinos during his tenure at the National Intelligence Service surpassed one billion dollars, most of which was deposited in foreign banks.

The Peruvian government sought his extradition as an alleged member of Montesino's Grupo Colina and responsible for 26-35 deaths or "disappearances" which the Truth and Reconciliation Commission (Peru) attributed to him.

[43] Montesinos was sentenced in September 2006 to a 20-year prison term for his direct involvement in an illegal arms deal to provide 10,000 assault weapons to Colombian rebels.

Tribunal judges made their ruling based on evidence that placed Montesinos at the center of an intricate web of negotiations designed to transport assault rifles from Jordan to the Revolutionary Armed Forces of Colombia FARC.

[44] In 2007 Montesinos was on trial for allegedly ordering the extra-judicial killings of the hostage-takers from the left-wing Túpac Amaru Revolutionary Movement (MRTA) during the 1997 Japanese embassy hostage crisis.

The former chief of the armed forces, Nicolas de Bari Hermoza [es], and retired Colonel Roberto Huaman were also charged with ordering the extrajudicial execution of the 14 rebels.

[49][50][51] In one reported audio, Montesinos mentions a first plan to have Fujimori's husband to go to the United States embassy in Lima to present "documentation of the fraud" to the Office of Regional Affairs and Central Intelligence Agency, with Montesinos allegedly saying he already contacted the embassy, that the documents would reach President Joe Biden and that his administration would condemn the election as interference from Cuba, Nicaragua, and Venezuela, subsequently giving Fujimori's claims of fraud more weight.

[49][52][53] In other reported audios, Montesinos suggests to retired military officer and Popular Force member Pedro Rejas Tataje on 10 June 2021 that they should bribe three electoral magistrates of the National Jury of Elections (JNE) – who were tasked with reviewing the narrow and controversial election – with one million dollars each, telling the former officer to contact attorney Guillermo Sendón who then reportedly made contact with JNE magistrate Luis Arce.